Abstract

The plasma technologies are widely used in metal surface engineering processes. Basically, these treatments improve the mechanical, tribological, and chemical properties of the material such as wear resistance, hardness, fatigue resistance, friction, and corrosion resistance. In this work, a comprehensive study of the influence of the microstructure on hardness of AISI P20 steel treated at different temperatures and times by pulsed plasma nitriding is reported. The processes were done by using a pulsed plasma industrial system. The samples were characterized by nano-indentation (hardness),x-ray diffraction(XRD),scanning electron microscopy(SEM), and x-ray dispersion spectroscopy (EDS). At lower treatmenttemperatures, a high density of small lamellar precipitates, constituted by more phase than phase, is formed. At intermediate treatmenttemperatures, big lamellar precipitates, constituted by more phase than phase, are formed at grain boundary. At higher treatmenttemperatures, the nitrided layer does not contain lamellar precipitates and it is only constituted by phase saturated in nitrogen. Hardness depends on size, shape, and distribution of precipitates and crystalline phases (microstructure). The higher hardness values are obtained when more and smaller lamellar precipitates are presented and constituted by more phase.

This work was sponsored by FAPESP, Project Nos. 04/01977-9 and 05/53926-1. E.A.O. is a FAPESP fellow. The authors are indebted to F. Alvarez and H. O. Pastore for the use of the LIITS and XRD measurements, respectively. The scanning electron microscopy work was performed with SEM JEOL JSM-5900LV and FEG-SEM JEOL JSM6330F microscopes of the LME/LNLS, Campinas-SP, Brazil.